Method for cleaning workpiece

ABSTRACT

A semiconductor cleaning method includes scrubbing a semiconductor wafer using a cleaning member made primarily of polyurethane and having micropores in a surface contacting the semiconductor wafer. The micropores have an average diameter ranging from 10 to 200 μm. The cleaning member may be made of either polyurethane foam or non-woven fabric composed of fibers bound together by urethane resin. By this scrubbing step, particles that are strongly attached to the surface of a substrate such as the semiconductor wafer can easily be removed. During cleaning of the substrate, surface irregularities and crystalline protrusions on the surface of a substrate such as a semiconductor wafer can be scraped off to adjust the surface roughness of the semiconductor wafer to a desired degree for making the semiconductor wafer surface flat.

This application is a continuation of now abandoned application, Ser.No. 08/434,754, filed May 4, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of and an apparatus forcleaning a workpiece, and more particularly to a method of and anapparatus for cleaning a substrate that needs to have a high degree ofcleanness, e.g., a semiconductor wafer, a glass substrate, a liquidcrystal panel, or the like.

2. Description of the Prior Art

As semiconductor devices have become more highly integrated in recentyears, circuit interconnections on semiconductor substrates have becomefiner and the distances between those circuit interconnections havebecome smaller. When semiconductor wafers are processed, small particlessuch as particles of semiconductor material, dust particles, crystallineprotrusive particles, or the like often tend to be attached to thesemiconductor wafers being processed. If a particle which is greater insize than the distance between interconnections exists on asemiconductor substrate, then the particle will short-circuitinterconnections on the semiconductor substrate. Therefore, anyundesirable particles on a semiconductor substrate have to besufficiently smaller than the distance between interconnections on thesemiconductor substrate. Such a problem and a requirement hold true forthe processing of other substrates including a glass substrate to beused as a mask, a liquid crystal panel, and so on. To meet the aboverequirement, there have been practiced some cleaning procedures forremoving fine particles or submicron particles off semiconductor wafers.

For example, it has heretofore been one practice to use a brush or asponge to scrub a semiconductor wafer. A scrubbing process using a brushof nylon, mohair, or the like is effective to remove particles havingdiameters of 1 μm or larger off semiconductor wafers. However, such ascrubbing process fails to produce an appreciable cleaning effect onsubmicron particles smaller than those particle sizes.

Particles having diameters of 0.2 μm or larger can be removed fromsemiconductor wafers by another scrubbing process using a sponge ofpolyvinyl alcohol (PVA). This scrubbing process is, however, ineffectivewhere particles are bonded to a semiconductor wafer with high bondingstrength. Another problem is that the sponge of PVA cannot beself-cleaned as particles are entrapped by the sponge.

Some semiconductor fabrication processes include a polishing step knownas a "water polishing step". The polishing step is employed to flattensurface irregularities on the surface of a semiconductor substrate whichare produced when various layers are deposited thereon.

The polishing step is carried out by a polishing apparatus whichcomprises a turntable and a top ring for holding a semiconductor waferto be polished. The surface of a semiconductor wafer to be polished ispressed against an abrasive cloth on the turntable by the top ring, andthe turntable and the top ring are rotated to move the semiconductorwafer and the abrasive cloth relative to each other. At the same time,an abrasive solution is supplied to the abrasive cloth to polish thesurface of the semiconductor wafer to a flat mirror finish.

In the water polishing step, the above polishing step is followed bysubsequently supplying water, instead of the abrasive solution, to theabrasive cloth to finish the polished surface of the semiconductor waferfor a desired level of surface roughness. The water polishing stepoffers an additional advantage in that the abrasive solution attached tothe semiconductor wafer at the time it is polished can be washed awayfrom the semiconductor wafer.

However, since the water polishing step is carried out after thesemiconductor wafer has been polished, remains of the used abrasivesolution, ground-off particles of the semiconductor wafer, and worn-offpieces of the abrasive cloth exist on the abrasive cloth and tend to beattached to the semiconductor wafer during the water polishing step.With the water polishing step alone, however, it is difficult to loweran attached amount of particles to a strict level required by the recentsemiconductor fabrication process.

The water polishing step suffers another drawback in that, since thewater polishing step is limited to the polishing step, it cannotgenerally be used for other purposes, e.g., cannot be applied to othersteps of a semiconductor fabrication process.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodof and an apparatus for effectively removing fine particles or submicronparticles from a substrate, removing particles strongly attached to asubstrate surface and microscratches on the substrate surface byscraping a thin layer off the substrate surface, holding particles whenthe substrate is cleaned, and self-cleaning a cleaning device after thesubstrate is cleaned.

According to the present invention, there is provided a method ofcleaning a workpiece, comprising the step of scrubbing a workpiece witha cleaning member made primarily of polyurethane and having microporesin a surface contacting the workpiece, the micropores having an averagediameter ranging from 10 to 200 μm.

According to the present invention, there is also provided a method ofcleaning a workpiece, comprising the step of scrubbing a workpiece witha cleaning member made of a synthetic resin and having micropores in asurface contacting the workpiece, the synthetic resin having a Shore Dhardness ranging from 30 to 80.

According to the present invention, there is further provided a methodof cleaning a substrate, comprising the step of scrubbing a substratewith a cleaning member made of one of polyurethane foam and non-wovenfabric composed of fibers bound together by urethane resin.

During the scrubbing step, a cleaning solution containing a surfactantmay be supplied to the workpiece in one aspect. Ammonia and hydrogenperoxide, hydrogen chloride and hydrogen peroxide may be supplied to theworkpiece in another aspect. A suspension composed of particles ofcolloidal silica suspended in an alkaline liquid may be supplied to theworkpiece in still another aspect.

According to the present invention, there is also provided an apparatusfor cleaning a substrate, comprising a spinning chuck for holding androtating a substrate, a supporting member positioned above the spinningchuck, and a cleaning member rotatably mounted on the supporting memberfor contacting and cleaning the substrate held by the spinning chuck,the cleaning member being made primarily of polyurethane and havingmicropores in a surface contacting the substrate, the micropores havingan average diameter ranging from 10 to 200 μm.

According to the present invention, there is also provided an apparatusfor cleaning a substrate, comprising a spinning chuck for holding androtating a substrate, a supporting member positioned above the spinningchuck, and a cleaning member rotatably mounted on the supporting memberfor contacting and cleaning the substrate held by the spinning chuck,the cleaning member being made of one of polyurethane foam and non-wovenfabric composed of fibers bound together by urethane resin.

With the arrangement of the present invention, it is possible to removeminute particles or submicron particles from a substrate such as asemiconductor wafer for thereby cleaning the semiconductor wafer highlyeffectively.

Particles that are strongly attached to the surface of a substrate suchas a semiconductor wafer can easily be removed by scrubbing.

At the same time a substrate is cleaned, surface irregularities andcrystalline protrusions on the surface of a substrate such as asemiconductor wafer can be scraped off to adjust the surface roughnessof the semiconductor wafer to a desired degree for making thesemiconductor wafer surface flat.

The cleaning member that is used to clean a substrate such as asemiconductor wafer can easily be self-cleaned after it has cleaned thesemiconductor wafer.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings which illustrate preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary perspective view of a cleaning apparatus forcarrying out a cleaning method according to the present invention;

FIG. 2 is an enlarged fragmentary cross-sectional view of a cleaningdevice of the cleaning apparatus;

FIG. 3 is an enlarged fragmentary cross-sectional view illustrative ofthe mechanism of the cleaning method according to the present invention;

FIG. 4 is an enlarged fragmentary perspective view showing a surface ofa cleaning member;

FIG. 5 is an enlarged fragmentary cross-sectional view of anothercleaning member;

FIG. 6 is a perspective view of a system composed of cleaning apparatusaccording to the present invention which are combined with a polishingapparatus for polishing semiconductor wafers; and

FIG. 7 is a vertical cross-sectional view of the polishing apparatusshown in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a cleaning apparatus for carrying out a cleaningmethod according to the present invention comprises a spinning chuck 2for holding a semiconductor wafer 1 and rotating the semiconductor wafer1 in a horizontal plane at a predetermined speed, and a rotatablecleaning device 6 incorporating a cleaning member 3 made of polyurethanefoam and having minute holes defined in a surface thereof. The cleaningapparatus further comprises a vertically movable swing arm 7 supportingon its free end the cleaning device 6 for moving the cleaning device 6over the semiconductor wafer 1 supported by the spinning chuck 2, acleaning solution nozzle 8 for ejecting a cleaning solution onto asurface, to be cleaned, of the semiconductor wafer 1, and a cleaning cup9 for cleaning the cleaning device 6. The swing arm 7 constitutes asupporting member for supporting the cleaning member 3. The cleaningdevice 6 is supported by a vertical rotatable shaft 10 on the free endof the swing arm 7, and can be rotated by the vertical rotatable shaft10 at a predetermined speed.

The semiconductor wafer 1 is loaded into the cleaning apparatus afterrelatively large particles have been removed by a rinsing process or ascrubbing process using a brush. The semiconductor wafer 1 is clamped bythe spinning chuck 2 with the surface to be cleaned of the semiconductorwafer 1 facing upwardly. At the same time the clamped semiconductorwafer 1 is rotated at a predetermined speed by the spinning chuck 2, acleaning solution is ejected from the cleaning solution nozzle 8 towardthe center of the semiconductor wafer 1.

The swing arm 7 is first in an initial position in which the cleaningdevice 6 supported thereon is placed in the cleaning cup 9. The cleaningdevice 6 is self-cleaned by soaking in a cleaning solution filled in thecleaning cup 9 when the cleaning device 6 is rotated in the cleaning cup9. After the cleaning device 6 is self-cleaned, the rotation of thecleaning device 6 is stopped, and the swing arm 7 is lifted to take thecleaning device 6 out of the cleaning cup 9. Then, the swing arm 7 isturned to move the cleaning device 6 to a position above the center ofthe semiconductor wafer 1. Thereafter, the arm 7 is lowered to press acleaning member 3 applied to the cleaning device 6 against the uppersurface of the semiconductor wafer 1. The cleaning device 6 starts torotate at a predetermined speed immediately before it contacts thesemiconductor wafer 1.

The cleaning member 3 of the cleaning device 6 as it is rotated aboutthe shaft 10 independently of the semiconductor wafer 1 is pressed bythe swing arm 7 against the upper surface of the semiconductor wafer 1while it is supported on and rotated by the spinning chuck 2. Then, thearm 7 is turned to angularly move the cleaning member 3 of the cleaningdevice 6 from the center of the semiconductor wafer 1 toward an outercircumferential edge of the semiconductor wafer 1 at a certain speed,thereby scrubbing the upper surface of the semiconductor wafer 1. Whenthe cleaning member 3 has reached the outer circumferential edge of thesemiconductor wafer 1, the swing arm 7 is stopped and then lifted toelevate the cleaning member 3 out of contact with the upper surface ofthe semiconductor wafer 1, thus completing one cycle of scrubbingoperation. The scrubbing operation is repeated by moving the swing arm 7again radially toward the center of the semiconductor wafer 1.

After at least one cycle of scrubbing operation has been carried out,the cleaning solution nozzle 8 stops ejecting the cleaning solution. Theswing arm 7 is moved to bring the cleaning device 6 to a position abovethe cleaning cup 9. Then, the swing arm 7 is lowered to place thecleaning device 6 into the cleaning cup 9. The cleaning device 6 isrotated in the cleaning cup 9 and self-cleaned by the cleaning solutionfilled in the cleaning cup 9.

The scrubbing operation is followed immediately by rotating the spinningchuck 2 at a high speed in a dry, inert gas atmosphere for therebyspin-drying the scrubbed semiconductor wafer 1.

The swing arm 7 is angularly moved from the center of the semiconductordevice 1 radially outwardly toward the outer circumferential edgethereof because the cleaning member 3 displaces contaminants andparticles on the upper surface of the semiconductor wafer 1 radiallyoutwardly in the same direction as centrifugal forces to which thosecontaminants and particles are subjected while the semiconductor wafer 1is being rotated by the spinning chuck 2.

As shown in FIG. 2, the cleaning device 6 is mounted on the lower end ofthe shaft 10. The cleaning device 6 comprises a cartridge 11 having alower surface to which the cleaning member 3 is applied. The cleaningmember 3 comprises a polishing abrasive cloth that is cut to a suitablesize. The polishing abrasive cloth has an adhesive seal on its reverseside which is bonded to the lower surface of the cartridge 11. Thecartridge 11 has a partly spherical concave surface slidably held incontact with a partly spherical convex surface of the shaft 10.Therefore, the polishing abrasive cloth is maintained in uniform contactwith the semiconductor wafer 1 even if the semiconductor wafer 1 clampedby the spinning chuck 2 is tilted or inclined.

The shaft 10 comprises an upper shaft member 10A and a lower shaftmember 10B which are connected coaxially to each other with acompression coil spring 12 interposed therebetween. The compression coilspring 12 normally urges the lower shaft member 10B to move away fromthe upper shaft member 10A for dampening forces to be applied throughthe shaft 10 and the cleaning device 6 to the semiconductor wafer 1while the cleaning device 6 is being held against the semiconductorwafer 1. Consequently, the cleaning member 3 can be kept in contact withthe upper surface of the semiconductor wafer 1 under uniform pressurewhile the semiconductor wafer 1 is being scrubbed. Furthermore, thesemiconductor wafer 1 is prevented from being damaged by undue forceswhich would be applied from the cleaning device 6 to the semiconductorwafer 1 when the semiconductor wafer 1 is tilted.

The polishing abrasive cloth of the cleaning member 3 is a commerciallyavailable polishing abrasive cloth that is generally used to polishsemiconductor wafers to a flat mirror finish. Examples of the polishingabrasive cloth are Suba 800 and IC-1000 manufactured by Rodel ProductsCorporation and Surfin xxx-5 and Surfin 000 manufactured by Fujimi Inc.The polishing abrasive cloth sold under the tradenames Suba 800, Surfinxxx-5, and Surfin 000 is made of non-woven fabric composed of fibersbound together by urethane resin, and the polishing abrasive cloth soldunder the tradename IC-1000 is made of polyurethane foam which is porousand has minute recesses or micropores in its surface.

The polishing abrasive cloth is used to polish semiconductor wafers, andhas a structure which tends to attract abrasive grain contained in thecleaning solution. Therefore, when the polishing abrasive cloth is usedto clean a semiconductor wafer, it is possible for the polishingabrasive cloth to remove easily those particles which are stronglyattached to the surface of the semiconductor wafer.

The mechanism of a cleaning method for removing particles from thesemiconductor wafer 1 with the cleaning member 3 composed of thepolishing abrasive cloth will be described below with reference to FIG.3.

FIG. 3 shows in enlarged cross section the cleaning member 3 forcleaning the semiconductor wafer 1. In FIG. 3, the polishing abrasivecloth C_(L) of the cleaning member 3 is made of polyurethane foam andhence has micropores "h" in its abrasive surface which is to be held incontact with the semiconductor wafer 1. The micropores "h" have a sizewhich may be selected from a range of various sizes depending on thepolishing abrasive cloth used, but preferably have an average sizeranging from 10 to 200 μm for cleaning the semiconductor wafer 1. Whenthe semiconductor wafer 1 and the polishing abrasive cloth C_(L) arepressed against each other and moved relative to each other, particles"p" on the semiconductor wafer 1 are scraped off by edges "e" of themicropores "h", trapped into the micropores "h", and removed away fromthe semiconductor wafer 1.

The particles "p" are shown in an exaggerated state in FIG. 3, and areactually much smaller than the micropores "h". Since the polyurethane isharder than the PVA sponge, it is considered to be able to effectivelyscrape particles off the semiconductor wafer 1. The polishing abrasivecloth has a Shore D hardness ranging from 30 to 80. This level ofhardness allows the polishing abrasive cloth to effectively scrapeparticles off the semiconductor wafer 1 without damaging thesemiconductor wafer 1. If a cleaning member of greater hardness wereused on the semiconductor wafer 1, it would damage the semiconductorwafer 1.

If the polishing abrasive cloth is pressed against the semiconductorwafer 1 under increased pressure, the polishing abrasive cloth itselfexhibits an abrasive action to scrape off the particles and also a thinsurface layer of the semiconductor wafer 1 to which the particles areattached. This is confirmed by the fact that the surface roughness ofthe semiconductor wafer 1 is smaller and hence its surface is smootherafter it has been scrubbed by the polishing abrasive cloth than beforeit is scrubbed by the polishing abrasive cloth.

The micropores in the surface of the polishing abrasive cloth areclosed, i.e., adjacent ones of those micropores are not joined to eachother. Accordingly, those particles which are removed from thesemiconductor wafer 1 and trapped in the micropores do not enter intothe interior of the cleaning member 3. Therefore, the particles trappedin the micropores can easily be removed, keeping the cleaning member 3clean.

After having scrubbed the semiconductor wafer 1, the cleaning member 3is typically self-cleaned by being rotated in the cleaning solutionfilled in the cleaning cup 9, as described above. However, the cleaningmember 3 may be cleaned by applying a water jet to the surface of thecleaning member 3 or ultrasonically vibrating the cleaning member 3.

While the cleaning member 3 has been described as being made ofpolyurethane foam, the cleaning member 3 may be made of non-woven fabriccomposed of fibers bound together by urethane resin. FIG. 4 shows atenlarged scale the surface of a piece of non-woven fabric composed offibers bound together by urethane resin. As shown in FIG. 4, fibers "f"are intertwined and bound or united together by urethane resin. Thenon-woven fabric has micropores "h" provided by interstices between thefibers "f". The micropores "h" serve to trap particles off thesemiconductor wafer 1 and remove them away from the semiconductor wafer1 in the same manner as the cleaning member 3 made of polyurethane foam.

FIG. 5 shows in enlarged cross section another cleaning member which ismade principally of polyurethane foam and has micropores in its surface,the surface being of a configuration which is different from that of thecleaning member shown in FIG. 3. The cleaning member shown in FIG. 5comprises a base "b" of non-woven fabric composed of fibers boundtogether by urethane resin, and a layer P_(L) of polyurethane foamdisposed on an upper surface of the base "b". The layer P_(L) ofpolyurethane foam has micropores "h", and includes a multiplicity offibers extending upwardly which are produced upon foaming of thepolyurethane. The cleaning member shown in FIG. 5 is used as a polishingabrasive cloth which is called a suede-type polishing abrasive cloth.The suede-type polishing abrasive cloth is particularly used forpolishing semiconductor wafers of silicon (Si), gallium arsenide (GaAs),or the like.

The suede-type polishing abrasive cloth is slightly softer than theaforesaid polishing abrasive cloth of polyurethane foam or non-wovenfabric composed of fibers bound together by urethane resin. However, thesuede-type polishing abrasive cloth is also capable of scraping a thinsurface layer off a substrate being cleaned. Since the suede-typepolishing abrasive cloth is used to finish a semiconductor wafer in thepolishing step, it is suitable for removing microscratches on thesurface of the semiconductor wafer.

The cleaning solution used in the cleaning method of cleaning thesemiconductor wafer with the cleaning member which is made primarily ofpolyurethane will be described below. By suitably selecting the cleaningsolution to be used in combination with the cleaning member which ismade primarily of polyurethane having micropores, it is possible toclean the semiconductor wafer with a composite cleaning effect thatincludes a mechanical cleaning effect based on scrubbing and a chemicalcleaning effect using the cleaning solution.

First, a cleaning solution comprising a surface-active agent will bedescribed below. A surfactant applied to a semiconductor wafer canweaken the force with which particles are attached to the surface of thesemiconductor wafer, thus allowing the particles to be removed easilyfrom the surface of the semiconductor wafer.

According to one mechanism in which particles are attached to thesurface of a semiconductor wafer, they are attached, together with afatty substance, i.e., an organic contaminant, to the surface of thesemiconductor wafer. In this case, molecules of a surfactant applied asa cleaning solution to the semiconductor wafer enter between the surfacethereof and the organic contaminant, engulf the organic contaminant, anddissolve it as oil droplets into the cleaning solution. Since theorganic contaminant that increases the force with which the particlesare attached to the surface of the semiconductor wafer is chemicallyremoved by the surfactant, the force with which the particles areattached to the surface of the semiconductor wafer is reduced, and hencethe particles can easily be removed from the surface of thesemiconductor wafer.

If the surfactant is used as the cleaning solution, then becausemolecules of the surfactant remain attached to the surface of thesemiconductor wafer, it is necessary to clean the surface of thesemiconductor wafer with an acid to remove the molecules of thesurfactant. Use of the surfactant as the cleaning solution inself-cleaning the cleaning member after it has scrubbed thesemiconductor wafer is also effective in reducing the force with whichparticles are attached to the cleaning member.

Second, a cleaning solution comprising a mixture of ammonia (NH₄ OH),hydrogen peroxide (H₂ O₂), and pure water (H₂ O) will be describedbelow.

The cleaning solution is capable of etching away a thin layer off thesurface of a substrate being cleaned, and is effective to remove organiccontaminants, metal ions, and so on.

The ammonia, hydrogen peroxide, and pure water should preferably bemixed at a ratio of 1:1:5. The cleaning solution has an increasedcleaning capability when heated.

Third, a cleaning solution comprising a mixture of hydrogen chloride(HCl), hydrogen peroxide (H₂ O₂), and pure water (H₂ O) will bedescribed below.

The cleaning solution is effective to dissolve and remove metal ions orthe like from the surface of a substrate being cleaned. When thesubstrate is contaminated by metal ions, ions of metals including sodium(Na), potassium (K), nickel (Ni), and iron (Fe) exist on the surface ofthe substrate. Since these contaminative metal ions affect electricproperties of the substrate, particularly a semiconductor wafer, theyshould preferably be removed completely.

The hydrogen chloride, hydrogen peroxide, and pure water shouldpreferably be mixed at a ratio of 1:1:5. The cleaning solution has anincreased cleaning capability when heated.

Fourth, a cleaning solution comprising a suspension composed ofparticles of colloidal silica (SiO₂) suspended in an alkaline liquidsuch as of potassium hydroxide (KOH) or sodium hydroxide (NaOH) will bedescribed below.

The cleaning solution is generally used as a polishing abrasivesolution. The colloidal silica is in the form of a particulate solid andhas a particle diameter of about 0.06 μm. If the cleaning solution is tobe supplied during a cleaning process, the particles of colloidal silicashould preferably have a uniform diameter.

Supplying the colloidal silica while a semiconductor wafer is beingcleaned appears to further contaminate the semiconductor wafer.Actually, however, the colloidal silica has a mechanical cleaning effectto remove the particles attached to the semiconductor wafer by collisionwith the particles of colloidal silica. Since the alkaline liquid isalso supplied, an organic contaminant can simultaneously be removed fromthe semiconductor wafer.

Inasmuch as the cleaning member can easily be self-cleaned, most of thecolloidal silica attached to the cleaning member can be removed in ashort period of time when the cleaning member is self-cleaned.Therefore, the cleaning member is repeatedly available for cleaningsemiconductor wafers using the above cleaning solution.

The above four types of cleaning solutions can be used independently orin combination to clean substrates.

The cleaning member which is made principally of polyurethane isresistant to erosion upon exposure to acids or alkalis. Consequently,the cleaning solution may comprise an acid or an alkali. Since thecleaning member can easily be self-cleaned, fine particles may be usedas a cleaning assistant.

FIG. 6 shows a system composed of cleaning apparatus according to thepresent invention which are combined with a polishing apparatus forpolishing semiconductor wafers. As shown in FIG. 6, the system comprisesa polishing apparatus 20, a wafer storage cassette 30, a feed robot 35,a first cleaning apparatus 40, and a second cleaning apparatus 45.

A polishing step which is carried out by the polishing apparatus 20 isone of the steps of a semiconductor fabrication process, and serves topolish a semiconductor wafer to a flat mirror finish. Wheninterconnections are to be formed as layers on the surface of asemiconductor wafer, the surface of the semiconductor wafer is polishedto a flat mirror finish before the layers are deposited, so that thelayers will subsequently be formed smoothly on the semiconductor wafer.

FIG. 7 shows the polishing apparatus 20 in detail. As shown in FIG. 7,the polishing apparatus 20 comprises a turntable 21 and a top ring 23for holding and pressing a semiconductor wafer 1 against the turntable21. The turntable 21 is coupled to a motor (not shown) and can berotated about its own axis in the direction indicated by the arrow. Apolishing abrasive cloth 24 is applied to the upper surface of theturntable 21 for contact with the semiconductor wafer 1. The polishingabrasive cloth 24 is made of the same material as that of the cleaningmember 3 shown in FIGS. 1 and 2.

The top ring 23 is coupled to a motor (not shown) and also to a cylinder(not shown) for vertically moving the top ring 23. Therefore, the topring 23 can be vertically moved in the directions indicated by thearrows and also can be rotated about its own axis, so that thesemiconductor wafer 1 can be pressed against the polishing abrasivecloth 24 under a desired pressure. An abrasive solution nozzle 25 ispositioned over the turntable 21 for supplying an abrasive solution Qonto the polishing abrasive cloth 24 attached to the upper surface ofthe turntable 21.

In operation, a semiconductor wafer 1 to be polished is conveyed fromthe wafer storage cassette 30 to the polishing apparatus 20 by the feedrobot 35. In the polishing apparatus 20, the semiconductor wafer 1 issupported on the lower surface of the top ring 23, and then pressedagainst the polishing abrasive cloth 24 on the upper surface of theturntable 21 while it is being rotated. The abrasive solution Q issupplied from the abrasive solution nozzle 25 onto the polishingabrasive cloth 24. The lower surface of the semiconductor wafer 1 isthus polished by the polishing abrasive cloth 24 with the abrasivesolution Q existing between the lower surface of the semiconductor wafer1 and the polishing abrasive cloth 24.

After having been polished, the semiconductor wafer 1 carries on itssurface abrasive grains contained in the abrasive solution Q andground-off particles of the semiconductor wafer 1, and is contaminatedby an alkaline metal of potassium (K) because the abrasive solution isof an alkaline base. These abrasive grains, particles and, contaminantshave to be cleaned away subsequently.

As shown in FIG. 6, the polished semiconductor wafer 1 is turned upsidedown to make the polished surface the upper side and conveyed by thefeed robot 35 to the first cleaning apparatus 40 in which thesemiconductor wafer 1 is scrubbed by a brush to remove most of theabrasive grains, particles, and contaminants from the surface of thesemiconductor wafer 1.

After the semiconductor wafer 1 has been cleaned by the cleaningapparatus 40, the semiconductor wafer 1 is fed to the second cleaningapparatus 45 before the surface of the semiconductor wafer 1 is dried.In the second cleaning apparatus 40, the semiconductor wafer 1 isscrubbed by the cleaning member according to the present invention toremove minute particles or submicron particles from the surface of thesemiconductor wafer 1 in the manner described above.

The cleaning method according to the present invention has beendescribed above in combination with the polishing step. However, thecleaning method according to the present invention may be any of varioussteps of the semiconductor fabrication process, e.g., an etching step ora chemical vapor deposition (CVD) step.

The present invention has been shown and described as being embodied forcleaning a semiconductor wafer. However, the principles of the presentinvention are also applicable to the cleaning of any of other substratesthat need to have a high degree of cleanness, e.g., a semiconductorwafer, a glass substrate, a liquid crystal panel, or the like.

The present invention offers the following advantages:

(1) It is possible to remove minute particles or submicron particlesfrom a substrate which cannot be removed by an ordinary scrubbing orchemical cleaning action, for thereby cleaning the substrate highlyeffectively. Consequently, semiconductor wafers, liquid crystal panels,or the like which have fine patterns can be produced with a high yield.

(2) Particles that are strongly attached to the surface of a substratecan easily be removed by scrubbing.

(3) At the same time a substrate is cleaned, the surface roughness ofthe substrate can be adjusted to a desired degree for making thesubstrate surface flat.

(4) A cleaning member that is used to clean a substrate can easily beself-cleaned after it has cleaned the substrate.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

What is claimed is:
 1. A method of cleaning a workpiece, comprising:at afirst cleaning station, performing a preliminary cleaning process toremove particles from a workpiece; transferring the workpiece from thefirst cleaning station to a second cleaning station having an abrasivecloth; holding the workpiece at the second cleaning station; and at thesecond cleaning station, cleaning the workpiece to remove, from theworkpiece, particles remaining on the workpiece after performance ofsaid preliminary cleaning process by scrubbing the workpiece with acleaning solution and said abrasive cloth of said second cleaningstation, wherein said abrasive cloth of said second cleaning stationconsists essentially of polyurethane and has micropores in a surfacecontacting said workpiece.
 2. A method according to claim 1, whereinsaidabrasive cloth of said second cleaning station is made of one ofpolyurethane foam and non-woven fabric composed of fibers bound togetherby urethane resin.
 3. A method according to claim 1, furthercomprising:rotating the workpiece during said cleaning of the workpieceat said second cleaning station.
 4. A method according to claim 1,whereinsaid cleaning of the workpiece at said second cleaning stationincludes at least one time of moving said abrasive cloth of said secondcleaning station from a center of the workpiece toward an outercircumferential edge of the workpiece.
 5. A method according to claim 1,further comprising:cleaning said abrasive cloth of said second cleaningstation, to remove therefrom the particles resulting from thepreliminary cleaning process and which became attached to said abrasivecloth of said second cleaning station during said cleaning of theworkpiece at said second cleaning station, by soaking said abrasivecloth of said second cleaning station in a cleaning solution when saidabrasive cloth of said second cleaning station is not being used toclean the workpiece.
 6. A method according to claim 1, wherein saidworkpiece comprises a semiconductor wafer.
 7. A method according toclaim 1, further comprising:drying said workpiece after said cleaning ofthe workpiece at said second cleaning station.
 8. A method according toclaim 7, whereinin said drying of the workpiece, the workpiece isrotated in a dry, inert gas atmosphere.
 9. A method to claim 1,whereinsaid holding of the workpiece at the second cleaning stationcomprises clamping the workpiece in a chuck.
 10. A method according toclaim 1, further comprising:rotating the workpiece at said secondcleaning station; and wherein said cleaning solution is supplied to theworkpiece at said second cleaning station.
 11. A method according toclaim 10, whereinsaid holding and said rotating of the workpiece at thesecond cleaning station comprise clamping the workpiece in a spinningchuck.
 12. A method according to claim 11, whereinsaid performing ofsaid preliminary cleaning process comprises scrubbing the workpiece witha brush.
 13. A method of cleaning a workpiece, comprising:at a firstcleaning station, performing a preliminary cleaning process to removeparticles from a workpiece; transferring the workpiece from the firstcleaning station to a second cleaning station having an abrasive cloth;holding the workpiece at the second cleaning station; and at the secondcleaning station, cleaning the workpiece to remove, from the workpiece,particles remaining on the workpiece after performance of saidpreliminary cleaning process by scrubbing the workpiece with a cleaningsolution and said abrasive cloth of said second cleaning station,wherein said abrasive cloth of said second cleaning station is made ofsynthetic resin and has micropores in a surface contacting saidworkpiece, said synthetic resin having a hardness selected from a ShoreD hardness ranging from 52 to 62, an Asker-C hardness of 80, a Shore Ahardness ranging from 58 to 68 and a Shore C hardness ranging from 61 to71.
 14. A method according to claim 13, whereinsaid abrasive cloth ofsaid second cleaning station is made of one of polyurethane foam andnon-woven fabric composed of fibers bound together by urethane resin.15. A method according to claim 13, further comprising:rotating theworkpiece during said cleaning of the workpiece at said second cleaningstation.
 16. A method according to claim 13, whereinsaid cleaning of theworkpiece at said second cleaning station includes at least one time ofmoving said abrasive cloth of said second cleaning station from a centerof the workpiece toward an outer circumferential edge of the workpiece.17. A method according to claim 13, further comprising:cleaning saidabrasive cloth of said second cleaning station, to remove therefrom theparticles resulting from the preliminary cleaning process and whichbecame attached to said abrasive cloth of said second cleaning stationduring said cleaning of the workpiece at said second cleaning station,by soaking said abrasive cloth of said second cleaning station in acleaning solution when said abrasive cloth of said second cleaningstation is not being used to clean the workpiece.
 18. A method accordingto claim 13, wherein said workpiece comprises a semiconductor wafer. 19.A method according to claim 13, further comprising:drying said workpieceafter said cleaning of the workpiece at said second cleaning station.20. A method according to claim 19, whereinin said drying of theworkpiece, the workpiece is rotated in a dry, inert gas atmosphere. 21.A method according to claim 13, whereinsaid holding of the workpiece atthe second cleaning station comprises the workpiece in a chuck.
 22. Amethod to claim 13, further comprising:rotating the workpiece at saidsecond cleaning station; and wherein said cleaning solution is suppliedto the workpiece at said second cleaning station.
 23. A method accordingto claim 22, whereinsaid holding and said rotating of the workpiece atthe second cleaning station comprise clamping the workpiece in aspinning chuck.
 24. A method according to claim 13, whereinsaidperforming of said preliminary cleaning process comprises scrubbing theworkpiece with a brush.
 25. A method of cleaning a workpiece,comprising:at a first cleaning station, performing a preliminarycleaning process to remove particles from a workpiece; transferring theworkpiece from the first cleaning station to a second cleaning stationhaving an abrasive cloth; holding the workpiece at the second cleaningstation; and at the second cleaning station, cleaning the workpiece toremove, from the workpiece, particles remaining on the workpiece afterperformance of said preliminary cleaning process by scrubbing theworkpiece with a cleaning solution and said abrasive cloth of saidsecond cleaning station, wherein said abrasive cloth of said cleaningstation is made of one of polyurethane foam and non-woven fabriccomposed of fibers bound together by urethane resin.
 26. A methodaccording to claim 25, further comprising:rotating the workpiece duringsaid cleaning of the workpiece at said second cleaning station.
 27. Amethod according to claim 25, whereinsaid cleaning of the workpiece atsaid second cleaning station includes at least one time of moving saidabrasive cloth of said second cleaning station from a center of theworkpiece toward an outer circumferential edge of the workpiece.
 28. Amethod according to claim 25, further comprising:cleaning said abrasivecloth of said second cleaning station, to remove therefrom the particlesresulting from the preliminary cleaning process and which becameattached to said abrasive cloth of said second cleaning station duringsaid cleaning of the workpiece at said second cleaning station, bysoaking said abrasive cloth of said second cleaning station in acleaning solution when said abrasive cloth of said second cleaningstation is not being used to clean the workpiece.
 29. A method accordingto claim 25, wherein said workpiece comprises a semiconductor wafer. 30.A method according to claim 25, further comprising:drying said workpieceafter said cleaning of the workpiece at said second cleaning station.31. A method according to claim 30, whereinin said drying of theworkpiece, the workpiece is rotated in a dry, inert gas atmosphere. 32.A method according to claim 25, whereinsaid holding of the workpiece atthe second cleaning station comprises clamping the workpiece in a chuck.33. A method according to claim 25, further comprising:rotating theworkpiece at said second cleaning station; and wherein said cleaningsolution is supplied to the workpiece at said second cleaning station.34. A method according to claim 33, whereinsaid holding and saidrotating of the workpiece at the second cleaning station compriseclamping the workpiece in a spinning chuck.
 35. A method according toclaim 25, whereinsaid performing of said preliminary cleaning processcomprises scrubbing the workpiece with a brush.
 36. A method of cleaninga workpiece, comprising:at a first cleaning station, performing apreliminary cleaning process to remove particles from a workpiece;transferring the workpiece from said first cleaning station to a secondcleaning station having an abrasive cloth; holding the workpiece at saidsecond cleaning station; and at said second cleaning station, cleaningthe workpiece to remove, from the workpiece, particles remaining on theworkpiece after performance of said preliminary cleaning process byscrubbing the workpiece with a cleaning solution and said abrasive clothof said second cleaning station; wherein said abrasive cloth is smallerthan the workpiece and is moved relative to the workpiece.
 37. A methodaccording to claim 36, whereinsaid abrasive cloth consists essentiallyof polyurethane and has micropores in a surface contacting saidworkpiece.
 38. A method according to claim 36, whereinsaid abrasivecloth is made of synthetic resin and has micropores in a surfacecontacting said workpiece, said synthetic resin having a hardnessselected from a Shore D hardness ranging from 52 to 62, an Asker-Chardness of 80, a Shore A hardness ranging from 58 to 68 and a Shore Chardness ranging from 61 to
 71. 39. A method according to claim 36,whereinsaid abrasive cloth is made of one of polyurethane foam andnon-woven fabric composed of fibers bound together by urethane resin.